Glucose uptake by cells is a critical process for maintaining cellular energy levels and ultimately, for tissue function and integrity. Increased glucose uptake has been shown to be cytoprotective in a number of settings. Increasing cellular glucose uptake also is advantageous in some metabolic conditions characterized by impaired glucose transport and in organs and tissues that have high energy requirements. An understanding of the mechanisms and pathways involved in cellular glucose uptake, thus, may permit the development of means for modulating the uptake process.
An important regulator of both glycolysis and glucose uptake in striated muscle is the AMP-activated protein kinase (AMPK). AMPK is a serine-threonine protein kinase that senses the cellular energy state, effecting multiple metabolic and non-metabolic pathways to increase cellular ATP production while also limiting energy consuming pathways (Young et. al., Trends Cardiovase Med 15, 110 (2005)). AMPK is regulated allosterically via AMP binding to its gamma regulatory subunit and by phosphorylation of Thr172 in the activating domain of the catalytic alpha subunit by upstream kinases, including LKB1 and CaMKKβ (Baron et al., Circ Res (2005)).
AMPK is activated under conditions that lead to inadequate blood flow and associated tissue ischemia, such as coronary artery disease. In the heart, AMPK directly stimulates PFK-2 activity and glycolysis (Marsin et al., Curr Biol 10, 1247 (2000)), induces GLUT4 translocation and increases ischemic glucose uptake preserves high energy phosphate content and limits myocardial injury and apoptosis (Russell, 3rd et al., J Clin Invest 114, 495 (2004)). AMPK also stimulates skeletal muscle glucose transport (Bergeron et al AJP 1999) through mechanism that is independent of the insulin signaling pathway; thus AMPK provides a target for the therapy of people with type 2 diabetes in whom the insulin stimulated pathway of glucose transport is impaired, leading to hyperglycemia. Since vascular disease, including coronary artery disease, peripheral arterial disease and cerebrovacular disease are highly prevalent in type 2 diabetes, AMPK represents a highly desirable target for both the treatment of the metabolic derangements of type 2 diabetes and the prevention of ischemic injury in these patients.
Accordingly, there is a critical need for methods and compositions for preventing cellular and tissue injury resulting from tissue ischemia. In particular, there is a need for methods and compositions for increasing cellular glucose uptake and preventing the depletion of energy stores during energetic stress associated with ischemia utilizing the AMPK pathway.